A transformer used for a switching power source apparatus such as an inverter and a DC-DC converter is disclosed in, for example, Japanese Unexamined Patent Application Publication No. H8-181023 (FIG. 1).
The transformer according to the related art shown in FIG. 1 has a coil bobbin 124 around which primary and secondary windings 134 and 135 are wound. At each end of a body 125 of the coil bobbin 124, there are outer flanges 128A and 128B each having a thick part 127. Between the outer flanges 128A and 128B, intermediate flanges 129, 130, 131, 132, and 133 are formed at predetermined intervals. Between the outer flange 128A and the first intermediate flange 129 adjacent to the outer flange 128A, the primary winding 134 is wound. Between the flange 130 that is spaced from the first intermediate flange 129 by a predetermined distance and the other outer flange 128B, the secondary winding 135 is wound. The secondary winding 135 is divided into a plurality of sections and is spaced from the primary winding 134 by the predetermined distance.
In the transformer having the above-mentioned structure, the primary winding 134 is wound between the outer flange 128A and the first intermediate flange 129. Away from this position by the predetermined distance, the secondary winding 135 is divided into a plurality of sections that are wound between the flanges 130–133. The primary winding 134 is intentionally spaced away from the secondary winding 135, to change the quantity of leakage inductance and capacitance between the primary and secondary windings and optimize a power factor.